1. Field of the Invention
The present invention relates to an X-ray radiator, of the type having a rotary X-ray tube with an allocated deflecting magnet system with at least one current-conducting coil for generating a magnetic deflecting field.
2. Description of the Prior Art
In X-rays radiators of the type described in U.S. Pat. No. 4,993,055, the complete X-ray tube rotates in a cooling medium which is enclosed by the radiator housing. For this reason, the emitter usually must emit the electrons on the axis of rotation, these electrons being accelerated by the high voltage between the emitter--which represents the cathode--and the anode. These electrons without further auxiliary means, i.e. if undeflected, would propagate straight ahead to the anode. To deflect the electron beam onto the provided focal spot outside the anode center, there needs to be an additional force on the electrons. This is produced by a magnetic field which is generated by the deflecting magnet system. The magnitude of the magnetic field becomes larger as the speed of the electrons increases, because of the Lorentz force. The deflection current which is carried by the coil and the high voltage of the X-ray tube thus have a functional connection.
Dependent on the different radiological applications, X-ray tubes are operated at different high voltages. As explained, in X-ray radiators with rotating bulb tubes, the deflecting current of the deflection system must be set dependent on the high voltage which is employed. Consequently, the control of the magnet system, i.e. the control of the coil current, must receive as a control signal representative of the level of the high voltage of the tube, so that the corresponding coil current can be set. Conventional X-ray radiators operate in such a way that the deflecting coil current is stored, as a function of the high voltage, in a database of the control computer for the radiator. Thus, by means of electronics and a controllable direct current source for the deflecting current, the deflecting current can be adjusted corresponding to the applied high voltage and can be fed to the X-ray radiator via additional cables. This control design is entirely acceptable for a new X-ray device. Problems arise, however, when an apparatus with a conventionally assembled X-ray tube is to be retrofitted to function as a rotating bulb X-ray radiator. Since these radiators are based on different characteristics, the voltage generator would also have to be retrofitted, so that the two elements are compatible and an adequate control of the radiator is possible. Although it would be possible to transmit, in turn, the high voltage signal at the generator side to the radiator as a separate signal via an additional line, this is disadvantageous to the extent that additional cable has to be laid and corresponding additional terminals have to be provided at the radiator itself.
German OS 31 36 881 and European Application 0 138 486 teach tapping a reference voltage which is proportional to the high voltage pending at an X-ray tube, for obtaining a focusing voltage corresponding to the high voltage, or for controlling an inverter.